[aidenn0]

Linux treats filenames as bytes and only disallows the ascii slash and null. All other bytes are fair game.

[cesarb]

> [...] and only disallows the ascii slash and null. All other bytes are fair game.

There's also the special treatment of "", ".", and ".." (that is, a file or directory name consisting entirely of zero, one, or two dots), and the convention that a name starting with a dot is hidden.

[inkyoto]

> and the convention that a name starting with a dot is hidden.

It is a UNIX shell implementation level convention. The file system and the kernel don't care, and a shell is not obliged to honour the convention.